Method and parking brake apparatus for an autonomously drivable vehicle

ABSTRACT

A parking brake apparatus is provided for an autonomously drivable vehicle having components of a parking brake system for applying a parking brake. The parking brake apparatus comprises a first controller arranged to provide one or more control signals to be applied to components of the parking brake system to apply the parking brake in response to a signal requesting the parking brake to be applied. The parking brake apparatus also comprises a second controller arranged to provide one or more control signals to be applied to other components of the parking brake system to apply the parking brake in response to unavailability of the first controller to cause the parking brake to be applied.

BACKGROUND

The present application relates to vehicle parking systems, and isparticularly directed to a method and parking brake apparatus for anautonomously drivable vehicle, such as for a parking system of anautonomously drivable commercial truck.

Vehicle parking systems for commercial trucks are known. One type ofvehicle parking system for trucks is an electronic parking system inwhich the parking brake is automatically applied using a primary parkingmechanism when certain criteria associated with the truck or the truckdriver are met. In some electronic parking systems, a second parkingmechanism as a backup is provided for applying the parking brake in theevent that the primary parking mechanism is unable to cause the parkingbrake to be applied. These known second parking mechanisms require thetruck driver to take some manual action to activate the secondaryparking mechanism after the truck driver is alerted that the primaryparking mechanism has been unable to cause the parking brake to beapplied.

The known secondary parking mechanisms can be used in any type of truckincluding autonomously drivable trucks. However, in the case of anautonomously driven truck, some manual action from an occupant of theautonomously driven truck would still be needed to activate thesecondary parking mechanism if the primary parking mechanism were unableto cause the parking brake to be applied. Accordingly, those skilled inthe art continue with research and development efforts in the field ofparking systems of a vehicle, such as a commercial truck, that includesa primary parking mechanism, and may or may not include a secondaryparking mechanism as a backup to the primary parking mechanism.

SUMMARY

In accordance with one embodiment, a parking brake apparatus is providedfor an autonomously drivable vehicle having components of a parkingbrake system for applying a parking brake. The parking brake apparatuscomprises a first controller arranged to provide one or more controlsignals to be applied to components of the parking brake system to applythe parking brake in response to a signal requesting the parking braketo be applied. The parking brake apparatus also comprises a secondcontroller arranged to provide one or more control signals to be appliedto other components of the parking brake system to apply the parkingbrake in response to unavailability of the first controller to cause theparking brake to be applied.

In accordance with another embodiment, a parking brake apparatus isprovided for an autonomously drivable vehicle having components of aparking brake system for applying a parking brake. The parking apparatuscomprises a primary parking brake controller arranged to control one ormore parking brake valves to enable one or more parking brake springs toapply the parking brake in response to a signal requesting the parkingbrake to be applied. The parking brake apparatus also comprises meansfor, when the vehicle is autonomously driven and without requiring anymanual action from an occupant of the autonomously driven vehicle,controlling the one or more parking brake valves to enable the one ormore parking brake springs to apply the parking brake when the primaryparking brake controller is unable to cause the parking brake to beapplied.

In accordance with still another embodiment, a computer-implementedmethod is provided for an autonomously drivable vehicle having a parkingbrake, a primary parking brake controller, and a secondary parking brakecontroller which is different from the primary parking brake controller.The computer-implemented method comprises detecting unavailability ofthe primary parking brake controller to cause the parking brake to beapplied. The method also comprises electronically by the secondaryparking brake controller, causing the parking brake to be applied inresponse to the unavailability of the primary parking brake controller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic block diagram showing an example parking brakeapparatus for an autonomously drivable vehicle, and constructed inaccordance with an embodiment.

FIG. 1B is a schematic block diagram similar to FIG. 1A, and showingparts in different positions.

FIG. 2 is a flow diagram depicting an example computer-implementedmethod for operating a parking brake apparatus in accordance with anembodiment.

FIG. 3A is a schematic block diagram showing an example parking brakeapparatus for an autonomously drivable vehicle, and constructed inaccordance with another embodiment.

FIG. 3B is a schematic block diagram similar to FIG. 3A, and showingparts in different positions.

DETAILED DESCRIPTION

The present application is directed to a parking brake apparatus for anautonomously drivable vehicle such as a commercial truck. The specificconstruction of the parking brake apparatus may vary. It is to beunderstood that the disclosure below provides a number of embodiments orexamples for implementing different features of various embodiments.Specific examples of components and arrangements are described tosimplify the present disclosure. These are merely examples and are notintended to be limiting.

Referring to FIG. 1A, a schematic block diagram showing an exampleparking brake apparatus 100 for an autonomously drivable vehicle, andconstructed in accordance with an embodiment is illustrated. In FIG. 1A,electrical line connections are shown as solid lines, pneumatic linesconnections are shown as dashed lines, and mechanical couplings areshown as double solid lines.

Parking brake apparatus 100 includes a controller area network (CAN) bus110 to which a number of vehicle devices are connected to communicatewith each other. The CAN bus 110 may be in a standardized serialcommunication format, such as SAE J1939, or in a proprietary format. Itis conceivable that some or all of the vehicle devices be hardwired forcommunication instead of using the CAN bus 110 for communication.

Vehicle devices that may be connected to the CAN bus 110 include, butare not limited to, a first controller as a primary parking brakecontroller 120, a second controller as a redundant parking brakecontroller 160, and a third controller as an automated driver controller180. The primary parking brake controller 120 may provide to the CAN bus110 a variety of signals including configuration messages, diagnosticstatus, and brake-specific signals such as parking brake status, andparking brake pressure. Similarly, the redundant parking brakecontroller 160 may provide to the CAN bus 110 a variety of signalsincluding configuration messages, diagnostic status, and brake-specificsignals such as parking brake status, and parking brake pressure. Theautomated driver controller 180 may provide to the CAN bus 110 a varietyof signals including configuration messages, diagnostic status, thedriving mode (i.e., autonomous, semi-autonomous, or driver-controlled),and desired intent of the status of the vehicle (e.g., stop, go, park).The CAN bus 110 enables the primary parking brake controller 120, theredundant parking brake controller 160, and the automated drivercontroller 180 to communicate with each other.

A primary compressed air supply 130 provides a source of compressed airin line 131 through a first 3/2 normally-open solenoid valve 134 andthen in line 135 to a first supply port 136 of a parking brake valve138. As an example, the parking brake valve 138 may comprise a valvesuch available as part of the Bendix Intellipark® system, commerciallyavailable from Bendix Commercial Vehicle Systems LLC located in Elyria,Ohio. The first 3/2 normally-open solenoid valve 134 is disposed betweenthe primary compressed air supply 130 and the parking brake valve 138.Similarly, a secondary compressed air supply 140 provides a source ofcompressed air in line 141 through a second 3/2 normally-open solenoidvalve 144 and then in a line 145 to a second supply port 146 of theparking brake valve 138. The second 3/2 normally-open solenoid valve 144is disposed between the secondary compressed air supply 140 and theparking brake valve 138. Each of the first and second 3/2 normally-opensolenoid valves 134, 144 may comprise a Bendix AT-3™ solenoid valve,commercially available from Bendix Commercial Vehicle Systems LLC.

Although the above description describes the use of a 3/2 normally-opensolenoid valve, it is conceivable that another type of valve may beused. For example, an antilock brake system (ABS) valve may be used,such as a Bendix M-40™ modulator valve, commercially available fromBendix Commercial Vehicle Systems LLC. For purpose of explanation, theuse of 3/2 normally-open solenoid valves will be described herein.

The primary parking brake controller 120 is in the form of an electroniccontroller unit that is arranged to monitor signals on the CAN bus 110to provide one or more control signals to apply the parking brake basedupon control logic 122 that is stored in a data storage unit of theprimary parking brake controller 120. The primary parking brakecontroller 120 provides one or more signals on lines 124, 125 to firstand second control ports 126, 127 of the parking brake valve 138 tocontrol delivery of compressed air (originating from first and secondcompressed air supplies 130, 140) to first and second delivery ports128, 129 of the parking brake valve 138.

The parking brake valve 138 is controlled by control logic 122 ofparking brake controller 120 to vary pneumatic pressure in line 142 toone or more chambers of spring brake chambers 143 and also to varypneumatic pressure in line 152 to trailer supply gladhands 154. Morespecifically, when the parking brake of the vehicle is applied, theprimary parking brake controller 120 provides one or more signals onlines 124, 125 to parking brake valve 138 so as to exhaust air in one ormore chambers of spring brake chambers 143. The spring brake chambers143 are operatively coupled via line 147 in known manner to parkingbrake springs 149. When air in spring brake chambers 143 is exhaustedand system air pressure drops to less than about 45 psi to 60 psi, theparking brake springs 149 are activated to apply the vehicle parkingbrake, as is known. Structure and operation of primary parking brakecontroller 120 and parking brake valve 138 for controlling operation ofspring brake chambers 143 and parking brake springs 149 to apply theparking brake are conventional and, therefore, will not be furtherdescribed.

At the same time the pneumatic pressure in line 142 to the one or morespring brake chambers 143 is varied to apply the parking brake, thepneumatic pressure in line 152 to the trailer supply gladhands 154(which are connectable to a trailer parking brake of the vehicle) isvaried to enable the trailer parking brake to be applied. Structure andoperation of primary parking brake controller 120 and parking brakevalve 138 for controlling operation of a trailer parking brake via thetrailer supply gladhands 154 are conventional and, therefore, will notbe further described.

One or more pressure-to-voltage transducers are coupled to correspondingone or more parking brake components. Each pressure-to-voltagetransducer provides a voltage indicative of pressure associated with thecorresponding parking brake component. More specifically, a firstpressure-to-voltage transducer 171 senses pressure in pneumatic line 142and provides a corresponding voltage on electrical line 175 to theprimary parking brake controller 120. A second pressure-to-voltagetransducer 172 senses pressure in pneumatic line 142 and provides acorresponding voltage on electrical line 176 to the redundant parkingbrake controller 160. A third pressure-to-voltage transducer 173 sensespressure in pneumatic line 152 and provides a corresponding voltage onelectrical line 177 to the primary parking brake controller 120. Afourth pressure-to-voltage transducer 174 senses pressure in pneumaticline 152 and provides a corresponding voltage on electrical line 178 tothe redundant parking brake controller 160.

The redundant parking brake controller 160 is in the form of anelectronic controller unit that is arranged to monitor signals on theCAN bus 110 to provide one or more control signals to apply the parkingbrake based upon control logic 162 that is stored in a data storage unitof the redundant parking brake controller 160. The redundant parkingbrake controller 160 provides a first control signal on line 164 to thefirst 3/2 normally-open solenoid valve 134 and a second control signalon 165 to the second 3/2 normally-open solenoid valve 142.

The automated driver controller 180 is in the form of an electroniccontroller unit that is arranged to monitor signals on the CAN bus 110indicating that the primary parking brake controller 120 is unavailableto apply the parking brake (or the trailer parking brake). The automateddriver controller 180 then provides one or more signals on the CAN bus110 to activate the redundant parking brake controller 160 to apply theparking brake.

In accordance with an aspect of the present disclosure, the redundantparking brake controller 160 and the automated driver controller 180cooperate to provide a backup parking brake solution in the event ofunavailability of the primary parking brake controller 120 to cause theparking brake to be applied. The automated driver controller 110monitors the primary parking brake controller 120, detectsunavailability of the primary parking brake controller 120 to cause theparking brake to be applied, and activates the redundant parking brakecontroller 160 to apply the parking brake when the unavailability isdetected. More specifically, the redundant parking brake controller 160has control logic 162 and the automated driver controller 180 hascontrol logic 182 that cooperates with the control logic 162 of theredundant parking brake controller 160 to provide the backup parkingbrake solution. Although shown separately, it is conceivable that theredundant parking brake controller 160 and the automated drivercontroller 180 may be combined as a single controller, and that thecontrol logic 162 and the control logic 182 may be combined as a singlecontrol logic block.

The first 3/2 normally-open solenoid valve 134 and the second 3/2normally-open solenoid valve 144 are shown in FIG. 1A in theirde-energized positions. In their de-energized positions shown in FIG.1A, compressed air is supplied through the parking brake valve 138 tothe spring brake chambers 143 and to the trailer supply gladhands 154.Both parking brakes (i.e., the parking brake of the truck tractor andthe parking brake of the truck trailer) are released (i.e., notapplied). When the primary parking brake controller 120 signals theparking brake valve 138 to apply the parking brakes, compressed air inline 142 and compressed air in line 152 are exhausted to atmosphere,which allows the parking brakes to be applied in known manner.

However, if the parking brakes do not apply in response to the primaryparking brake controller 120 to do so, the redundant parking brakeprocessor 160 and the automated driver controller 180 cooperate toenergize the first 3/2 normally-open solenoid valve 134 and the second3/2 normally-open solenoid valve 144 so as to move them to theirenergized positions shown in FIG. 1B. In their energized positions shownin FIG. 1B, compressed air from the primary compressed air supply 130and compressed air from the secondary compressed air supply 140 areblocked by the first and second 3/2 normally-open solenoid valves 134,144 from reaching the parking brake valve 138 to enable the parkingbrakes to be applied when the primary parking brake controller 120signals the parking brake valve 138 to do so. When compressed air isblocked from reaching the spring brake chambers 143 and the trailersupply gladhands 154, the parking brakes are applied.

More specifically, program instructions of a secondary parking brakecontrol algorithm associated with the control logic 162 of the redundantparking brake controller 160 and the control logic 182 of the automateddriver controller 180 are executed to provide a backup for the controllogic 122 of the primary parking brake controller 120 in the event thatthe parking brakes are not applied in response to execution of programinstructions of a primary parking brake control algorithm associatedwith the control logic 122 of the primary parking brake controller 120.

The unavailability of the parking brakes to be applied can be due to anumber of reasons. One reason may be that the primary parking brakecontroller 120 does not execute program instructions of the primaryparking brake control algorithm to apply the parking brakes in responseto a signal requesting the parking brakes to be applied. Another reasonmay be that one or more control signals from the primary parking brakecontroller 120 do not reach parking brake components so that the parkingbrakes can be applied. Yet another reason may be due to unresponsivenessof a portion of the parking brake valve 138 (e.g., an internal relayvalve of the parking brake valve 138). Still another reason may be dueto loss of communication between certain vehicle components includingcomponents of the parking brake system. Other reasons for unavailabilityof the parking brakes to be applied are possible.

Referring to FIG. 2, a flow diagram 200 depicts an examplecomputer-implemented method of operating a parking brake apparatus inaccordance with an embodiment. The computer-implemented method is for anautonomously drivable vehicle having a parking brake, a primary parkingbrake controller, and a secondary parking brake controller which isdifferent from the primary parking brake controller.

In block 210, the process begins by detecting unavailability of theprimary parking brake controller to cause the parking brake to beapplied. The detecting may be performed by looking at the memory of theprimary parking brake controller or at a CAN bus for a signal that isindicative of unavailability of the parking brake to be applied inresponse the primary parking brake controller to do so. Then, in block220, the secondary parking brake controller responds by causing theparking brake to be applied in response to the unavailability of theprimary parking brake controller. As an example, the secondary parkingbrake controller is responsive to the primary parking brake controllersending a signal stating that it is unavailable. As another example, thesecondary parking brake controller is responsive to the primary parkingbrake controller simply not communicating at all when the secondaryparking brake controller sees that the vehicle needs to park (e.g., whenthe secondary parking brake controller sees a message from an automateddriver controller indicating that the vehicle needs to park). Theprocess then ends.

In some embodiments, the secondary parking brake controller causes theparking brake to be applied when the unavailability of the primaryparking brake controller to cause the parking brake to be applied is dueto inability of the primary parking brake controller to provide one ormore control signals for applying to one or more parking brake valves toenable one or more parking brake springs to apply the parking brake.

In some embodiments, the secondary parking brake controller causes theparking brake to be applied when the unavailability of the primaryparking brake controller to cause the parking brake to be applied is dueto inability of one or more control signals from the primary parkingbrake controller to reach one or more parking brake valves to enable oneor more parking brake springs to apply the parking brake.

In some embodiments, the secondary parking brake controller causes theparking brake to be applied when the unavailability of the primaryparking brake controller to cause the parking brake to be applied is dueto absence of response of a parking brake valve of the parking brakesystem.

In some embodiments, unavailability of the primary parking brakecontroller to cause the parking brake to be applied is detected by thesecondary parking brake controller receiving a signal from the primaryparking brake controller stating that the primary parking brakecontroller is unavailable.

In some embodiments, unavailability of the primary parking brakecontroller to cause the parking brake to be applied is detected by thesecondary parking brake controller receiving a signal from an autonomousdriver controller stating that the primary parking brake controller isunavailable.

In some embodiments, the method is performed by a processor having amemory executing one or more programs of instructions which are tangiblyembodied in a program storage medium readable by the processor.

Program instructions for enabling the secondary parking brake controller(e.g., the redundant parking brake controller 160 together with theautomated driver controller 180 shown in FIGS. 1A and 1B) to performoperation steps in accordance with the flow diagram 200 shown in FIG. 2may be embedded in memory internal to the controllers. Alternatively, orin addition to, program instructions may be stored in memory external tothe controllers. As an example, program instructions may be stored inmemory internal to a different electronic controller unit of thevehicle. It is conceivable that any number of electronic controllerunits may be used. Moreover, it is conceivable that any type ofelectronic controller unit may be used. Suitable electronic controllerunits for use in vehicles are known and, therefore, have not beendescribed. Accordingly, the program instructions of the presentdisclosure can be stored on program storage media associated with one ormore vehicle electronic controller units. Program instructions may bestored on any type of program storage media including, but not limitedto, external hard drives, flash drives, and compact discs. Programinstructions may be reprogrammed depending upon features of theparticular electronic controller unit.

A second embodiment of a parking brake apparatus is illustrated in FIGS.3A and 3B. Since the embodiment illustrated in FIGS. 3A and 3B isgenerally similar to the embodiment illustrated in FIGS. 1A and 1B,similar numerals are utilized to designate similar components, thesuffix letter “a” being associated with the embodiment of FIGS. 3A and3B to avoid confusion.

Parking brake apparatus 100 a comprises primary parking brake controller120 a, redundant parking brake controller 160 a, and automated drivercontroller 180 a. Primary parking brake controller 120 a controlsoperation of parking brake valve 138 a and spring brake chambers 143 ain similar manner that primary parking brake controller 120 controlsparking brake valve 138 and spring brake chambers 143 as describedhereinabove in the embodiment of FIGS. 1A and 1B.

Similarly, redundant parking brake controller 160 a controls operationof first and second 3/2 normally-open solenoid valves 134 a, 144 a insimilar manner that redundant parking brake controller 160 controlsoperation of first and second 3/2 normally-open solenoid valves 134, 144as described hereinabove in the embodiment of FIGS. 1A and 1B. Automateddriver controller 180 a communicates with primary parking brakecontroller 120 a and redundant parking brake controller 160 a in samemanner that automated driver controller 180 communicates with primaryparking brake controller 120 and redundant parking brake controller 160as described hereinabove in the embodiment of FIGS. 1A and 1B.

In the embodiment of FIGS. 3A and 3B, a first relay valve 310 isdisposed between first 3/2 normally-open solenoid valve 134 a andparking brake valve 138 a. Similarly, a second relay valve 320 isdisposed between second 3/2 normally-open solenoid valve 144 a andparking brake valve 138 a.

Compressed air is supplied from primary compressed air supply 130 a inline 131 a to first 3/2 normally-open solenoid valve 134 a and then inline 312 to control port 313 of first relay valve 310. Pneumatic line315 interconnects delivery port 314 of first relay valve 310 and supplyport 136 a of parking brake valve 138 a. Compressed air is also suppliedfrom primary compressed air supply 130 a in line 316 to supply port 318of first relay valve 310.

Compressed air is supplied from secondary compressed air supply 140 a inline 141 a to second 3/2 normally-open solenoid valve 144 a and then inline 322 to control port 323 of second relay valve 320. Pneumatic line325 interconnects delivery port 324 of second relay valve 320 and supplyport 146 a of parking brake valve 138 a. Compressed air is also suppliedfrom secondary compressed air supply 140 a in line 326 to supply port328 of second relay valve 320.

In the event that primary parking brake controller 120 a is unavailableto cause the parking brake to be applied, redundant parking brakecontroller 160 a and automated driver controller 180 a cooperate toenergize first and second 3/2 normally-open solenoid valves 134 a, 144 ato move them from their de-energized positons shown in FIG. 3A to theirenergized positions shown in FIG. 3B to apply the parking brake in thesame manner as described hereinabove in the embodiment of FIGS. 1A and1B. However, in the embodiment shown in FIGS. 3A and 3B, the use offirst and second relay valves 310, 320 in conjunction with first andsecond 3/2 normally-open solenoid valves 134 a, 144 a increasescompressed air flow capacity to parking brake valve 138 a to apply theparking brake while reducing the electrical power needed to energizefirst and second 3/2 normally-open solenoid valves 134 a, 144 a.

It should be apparent that the above description describes a backupparking brake system for a main parking brake system of an autonomouslydriven vehicle that may or may not have a human “driver” occupying theautonomously driven vehicle. If a human driver is occupying theautonomously driven vehicle, the human driver is not an integral part ofthe backup parking brake system (i.e., no manual action is required fromthe human driver to activate the backup parking brake system in theevent of unavailability of the main parking brake system to apply theparking brake). Accordingly, the backup parking brake system causes theparking brake to be applied when the main parking brake system is unableto cause the parking brake to be applied, such as when a control signalis unable to reach a parking brake valve or when a parking brake valveis unresponsive.

It should also be apparent that the parking brake control algorithmsassociated with the parking brake apparatus 100 of FIGS. 1A and 1B andthe parking brake apparatus 100 a of FIGS. 3A and 3B are integrated intoa practical application of implementing a low-cost backup parking brakemechanism for autonomously drivable vehicles. The backup parking brakemechanism is low cost since implementation requires the addition ofessentially only a pair of 3/2 normally-open solenoid valves and a pairof controllers (or just a single controller if the redundant parkingbrake controller and the automated driver controller are combined).

A number of advantages result by providing an autonomously drivablevehicle with the above-described parking brake apparatus 100 of FIGS. 1Aand 1B (and the parking brake apparatus 100 a of FIGS. 3A and 3B) toprovide the backup parking brake mechanism.

One advantage is that, even if the main parking brake system were to beunavailable, service brake pressure can be retained (i.e., does not needto be exhausted to atmosphere) so that the service brake can continue tohold the vehicle if needed. This eliminates the need to unloadcompressed air or the need to shut down the vehicle engine.

Another advantage is that since the first and second 3/2 normally-opensolenoid valves 134, 144 are controlled by one controller (i.e., theredundant parking brake controller 160), there is no need to coordinatesolenoid valve diagnostics between two controllers. This simplifiesparking brake system design, and facilitates troubleshooting whenservicing of the parking brake mechanisms is needed.

Still another advantage is that since two pressure-to-voltagetransducers 171, 172 are coupled to pneumatic line 142 to the springbrake chambers 143, an independent indication of air pressure in springbrake chambers 143 is provided. Similarly, since two pressure-to-voltagetransducers 173, 174 are coupled to pneumatic line 154 to the trailersupply gladhands 154, an independent indication of air pressure intrailer supply gladhands 154 is provided. This is advantageous becauseadditional information may be used to satisfy additional functionalsafety requirements of the system.

Moreover, although the above description describes the use ofpressure-to-voltage transducers 171, 172, 173, 174, it is conceivablethat other types of transducers may be used, such as wheelspeed-to-voltage transducers (i.e., wheel speed sensors). As an example,with the use of wheel speed sensors (either alone or in conjunction withpressure-to-voltage transducers), it is possible to monitor for thefollowing sequence of events: (1) the vehicle is stationary with theparking brake released, (2) the vehicle is stationary with the mainparking brake system indicating the parking brake is activated, and (3)the vehicle is moving with the main parking brake system indicating theparking brake is activated. Observation of this sequence of eventsindicates a rollaway-from-park rather than a rollaway due tounavailability or inability of the parking brake to be applied whenneeded. If this occurs, the automated driver controller 180 could usethe service brake to stop the vehicle or use the backup parking brakesystem to attempt to park the vehicle while continuing to monitor thewheel speed sensors to determine whether the vehicle is remainingstationary.

Aspects of disclosed embodiments may be implemented in software,hardware, firmware, or a combination thereof. The various elements ofthe system, either individually or in combination, may be implemented asa computer program product tangibly embodied in a machine-readablestorage device for execution by a processor. Various steps ofembodiments may be performed by a computer processor executing a programtangibly embodied on a computer-readable medium to perform functions byoperating on input and generating output. The computer-readable mediummay be, for example, a memory, a transportable medium such as a compactdisk or a flash drive, such that a computer program embodying aspects ofthe disclosed embodiments can be loaded onto a computer.

While the present invention has been illustrated by the description ofexample processes and system components, and while the various processesand components have been described in detail, applicant does not intendto restrict or in any way limit the scope of the appended claims to suchdetail. Additional modifications will also readily appear to thoseskilled in the art. The invention in its broadest aspects is thereforenot limited to the specific details, implementations, or illustrativeexamples shown and described. Accordingly, departures may be made fromsuch details without departing from the spirit or scope of applicant'sgeneral inventive concept.

What is claimed is:
 1. A parking brake apparatus for an autonomouslydrivable vehicle having components of a parking brake system forapplying a parking brake, the parking brake apparatus comprising: afirst controller arranged to provide one or more control signals to beapplied to components of the parking brake system to apply the parkingbrake in response to a signal requesting the parking brake to beapplied; and a second controller arranged to provide one or more controlsignals to be applied to other components of the parking brake system toapply the parking brake in response to unavailability of the firstcontroller to cause the parking brake to be applied.
 2. A parking brakeapparatus for an autonomously drivable vehicle according to claim 1,wherein (i) the first controller is arranged to execute programinstructions of a primary parking brake control algorithm to apply theparking brake in response to the signal requesting the parking brake tobe applied, and (ii) the second controller is arranged to executeprogram instructions of a secondary parking brake control algorithm toapply the parking brake in response to unavailability of the firstcontroller to execute program instructions of the primary parking brakecontrol algorithm to apply the parking brake in response to the signalrequesting the parking brake to be applied.
 3. A parking brake apparatusfor an autonomously drivable vehicle according to claim 1, wherein (i)the first controller is arranged to execute program instructions of aprimary parking brake control algorithm to apply the parking brake inresponse to the signal requesting the parking brake to be applied, and(ii) the second controller is arranged to execute program instructionsof a secondary parking brake control algorithm to apply the parkingbrake in response to inability of the one or more control signals fromthe first controller to reach components of the parking brake system. 4.A parking brake apparatus for an autonomously drivable vehicle accordingto claim 1, wherein (i) the first controller is arranged to executeprogram instructions of a primary parking brake control algorithm toapply the parking brake in response to the signal requesting the parkingbrake to be applied, and (ii) the second controller is arranged toexecute program instructions of a secondary parking brake controlalgorithm to apply the parking brake in response to unresponsiveness ofa parking brake valve of the parking brake system.
 5. A parking brakeapparatus for an autonomously drivable vehicle according to claim 1further comprising: a parking brake valve controllable by the firstcontroller; a first 3/2 normally-open solenoid valve disposed between aprimary compressed air supply and the parking brake valve; and a second3/2 normally-open solenoid valve disposed between a secondary compressedair supply and the parking brake valve; wherein the second controller isarranged to provide a first control signal to the first normally-open3/2 solenoid valve, and a second control signal to the secondnormally-open 3/2 solenoid valve.
 6. A parking brake apparatus for anautonomously drivable vehicle according to claim 5 further comprising: afirst relay valve disposed between the first 3/2 normally-open solenoidvalve and the parking brake valve; and a second relay valve disposedbetween the second 3/2 normally-open solenoid valve and the parkingbrake valve.
 7. A parking brake apparatus for an autonomously drivablevehicle according to claim 1 further comprising: a third controllerarranged to (i) monitor the first controller, (ii) detect unavailabilityof the first controller to cause the parking brake to be applied, and(iii) activate the second controller to provide one or more controlsignals to be applied to components of the parking brake system to applythe parking brake in response to detecting unavailability of the firstcontroller to cause the parking brake to be applied.
 8. A parking brakeapparatus for an autonomously drivable vehicle according to claim 7,wherein the second controller and the third controller comprise a singlecontroller.
 9. A parking brake apparatus for an autonomously drivablevehicle according to claim 7 further comprising: a controller areanetwork (CAN) bus that enables the first, second, and third controllersto communicate with each other.
 10. A parking brake apparatus for anautonomously drivable vehicle according to claim 1 further comprising:one or more pressure-to-voltage transducers coupled to corresponding oneor more components of the parking brake system, wherein eachpressure-to-voltage transducer provides a voltage indicative of pressureassociated with the corresponding component of the parking brake system.11. A parking brake apparatus for an autonomously drivable vehiclehaving components of a parking brake system for applying a parkingbrake, the parking apparatus comprising: a primary parking brakecontroller arranged to control one or more parking brake valves toenable one or more parking brake springs to apply the parking brake inresponse to a signal requesting the parking brake to be applied; andmeans for, when the vehicle is autonomously driven and without requiringany manual action from an occupant of the autonomously driven vehicle,controlling the one or more parking brake valves to enable the one ormore parking brake springs to apply the parking brake when the primaryparking brake controller is unable to cause the parking brake to beapplied.
 12. A parking brake apparatus for an autonomously drivablevehicle according to claim 11, wherein the means includes a redundantparking brake controller arranged to control the one or more parkingbrake valves to enable the one or more parking brake springs to applythe parking brake when the primary parking brake controller is unable tocause the parking brake to be applied.
 13. A parking brake apparatus foran autonomously drivable vehicle according to claim 12, wherein themeans includes an autonomous driver controller arranged to (i) monitorthe primary parking brake controller, (ii) detect when the primaryparking brake controller is unable to respond to the signal requestingthe parking brake to be applied, and (iii) activate the redundantparking brake controller to control the one or more parking brake valvesto enable the one or more parking brake springs to apply the parkingbrake when the primary parking brake controller is detected to be unableto cause the parking brake to be applied.
 14. A parking brake apparatusfor an autonomously drivable vehicle according to claim 12, wherein themeans includes an autonomous driver controller arranged to (i) monitorthe primary parking brake controller, (ii) detect when one or morecontrol signals from the primary parking brake controller is unable toreach one or more components of the parking brake system, and (iii)activate the redundant parking brake controller to control one or moreparking brake valves to enable the one or more parking brake springs toapply the parking brake when the one or more control signals from theprimary parking brake controller is detected to be unable to reach theone or more components of the parking brake system.
 15. A parking brakeapparatus for an autonomously drivable vehicle according to claim 12,wherein the means includes an autonomous driver controller arranged to(i) monitor the primary parking brake controller, (ii) detect when aportion of a parking brake valve of the parking brake system isunresponsive, and (iii) activate the redundant parking brake controllerto control the one or more parking brake valves to enable the one ormore parking brake springs to apply the parking brake whenunresponsiveness of the portion of the parking brake valve of theparking brake system is detected.
 16. A computer-implemented method foran autonomously drivable vehicle having a parking brake, a primaryparking brake controller, and a secondary parking brake controller whichis different from the primary parking brake controller, thecomputer-implemented method comprising: detecting unavailability of theprimary parking brake controller to cause the parking brake to beapplied; and electronically by the secondary parking brake controller,causing the parking brake to be applied in response to theunavailability of the primary parking brake controller.
 17. Acomputer-implemented method according to claim 16, whereinelectronically by the secondary parking brake controller, causing theparking brake to be applied in response to the unavailability of theprimary parking brake controller includes: electronically by thesecondary parking brake controller, causing the parking brake to beapplied when the unavailability of the primary parking brake controllerto cause the parking brake to be applied is due to inability of theprimary parking brake controller to provide one or more control signalsfor applying to one or more parking brake valves to enable one or moreparking brake springs to apply the parking brake.
 18. Acomputer-implemented method according to claim 16, whereinelectronically by the secondary parking brake controller, causing theparking brake to be applied in response to the unavailability of theprimary parking brake controller includes: electronically by thesecondary parking brake controller, causing the parking brake to beapplied when the unavailability of the primary parking brake controllerto cause the parking brake to be applied is due to inability of one ormore control signals from the primary parking brake controller to reachone or more parking brake valves to enable one or more parking brakesprings to apply the parking brake.
 19. A computer-implemented methodaccording to claim 16, wherein electronically by the secondary parkingbrake controller, causing the parking brake to be applied in response tothe unavailability of the primary parking brake controller includes:electronically by the secondary parking brake controller, causing theparking brake to be applied when the unavailability of the primaryparking brake controller to cause the parking brake to be applied is dueto absence of response of a parking brake valve of the parking brakesystem.
 20. A computer-implemented method according to claim 16, whereindetecting unavailability of the primary parking brake controller tocause the parking brake to be applied includes: electronically by thesecondary parking brake controller, receiving a signal from the primaryparking brake controller stating that the primary parking brakecontroller is unavailable.
 21. A computer-implemented method accordingto claim 16, wherein detecting unavailability of the primary parkingbrake controller to cause the parking brake to be applied includes:electronically by the secondary parking brake controller, receiving asignal from an autonomous driver controller stating that the primaryparking brake controller is unavailable.
 22. A computer-implementedmethod according to claim 16, wherein the method is performed by aprocessor having a memory executing one or more programs of instructionswhich are tangibly embodied in a program storage medium readable by theprocessor.